Relevant parts of this background description are also a part of embodiments of the disclosed invention.
Several floor panels on the market are installed in a floating manner with mechanical locking systems formed at the long and short edges. These systems comprise locking means, which lock the panels horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the panel. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminium or plastic material, which is integrated with the floor panel, i.e. joined with the floor panel in connection with the manufacture thereof.
Laminate flooring usually comprise a 6-8 mm wood based core, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1 mm thick lower balancing layer. The laminate surface and the balancing layer comprise melamine-impregnated paper. The most common core material is fibreboard with high density and good stability usually called HDF—High Density Fibreboard. The impregnated surface and balancing papers are laminated to the core with heat and pressure. HDF material is hard and has a low flexibility especially in the vertical direction perpendicular to the fibre orientation.
Recently a new type of powder based laminate floors has been introduced. Impregnated paper is replaced with a dry powder mix comprising wood fibres, melamine particles, aluminium oxide and pigments. The powder is applied on an HDF core and cured under heat and pressure. Generally high quality HDF is used with a high resin content and low water swelling. Advanced decors may be formed with digital printing. Water based ink is injected into the powder prior to pressing.
Luxury vinyl tile, LVT, flooring with a thickness of 3-6 mm usually comprises a transparent wear layer which may be coated with an ultraviolet, UV, cured polyurethane, PU, lacquer and a decorative plastic foil under the transparent foil. The wear layer and the decorative foil are laminated to one or several core layers comprising a mix of thermoplastic material and mineral fillers. The plastic core may be rather soft and flexible but also rather rigid depending on the filler content.
Wood Plastic Composite floors generally referred to as WPC floors are similar to LVT floors. The core comprises thermosetting material mixed with wood fibre fillers and is generally stronger and much more rigid than the mineral based LVT core.
Thermoplastic material such as PVC, PP or PE may be combined with a mix of wood fibres and mineral particles and this may provide a wide variety of floor panels with different densities and flexibilities.
Moisture resistant HDF with a high resin content, and WPC floors comprise stronger and more flexible core materials than conventional HDF based laminate floors and they are generally produced with a lower thickness.
The above mentioned floor types comprise different core materials with different flexibility, density and strengths. Locking systems formed in one piece with the core must be adapted to such different material properties in order to provide a strong and cost efficient locking function.